Situations arise where a well is to be abandoned and the wellhead is to be recovered. In other circumstances, the casing needs to be cut and it is desirable to perform the cut while the casing is in tension. In situations where the casing is to be cut below the wellhead, various tools have been employed in the past to allow application of a tensile force to the casing, while a cutter rotates to cut the casing. Generally speaking, these tools have taken a grip within the seal bore area of the wellhead by attempting to engage grooves or threads adjacent the internal seal bore of the wellhead. These devices have proven to be potentially troublesome if the engagement with the internal groove or thread is not accomplished properly. As a result, the cutter can spin, within the wellhead, and disengage the connection to the wellhead which provides the tensile load on the casing all during the cutting operation.
Another problem encountered with previous devices is the large assortment of dimensional relationships in wellheads. Thus, for prior designs, involving a spear to be used to apply the tensile load to the casing, the distance from where the portion of the spear stops its movement to where the gripping member is positioned at that time, might need to be altered depending on the particular wellhead. As a result, in the past, specific tools were required for specific geometrical relationships. One of the objects of the present invention is to provide a multi-purpose tool which can accommodate different dimensional relationships in wellheads so as to accomplish a cutting of the casing while under an overpull regardless of the internal wellhead configurations.
Clutching mechanisms have been used for facilitation of the grip of the spear holding the rotary cutter and for its ultimate release. However, prior designs have allowed the clutching assembly to be located within the wellhead while the cutting operation proceeds. The disadvantage of such a configuration was that when the cuttings are circulated out of the wellhead, they tend to lodge in the clutching mechanism if the clutching mechanism is still in the return fluid stream. Thereafter, disengagement of the device from the wellhead becomes problematic as the clutch mechanism fails due to clogging or plugging with casing cuttings.
Certain prior designs illustrating some of the shortcomings mentioned above are illustrated in U.S. Pat. No. 4,969,514 as well as a product called 2M Rotating Spear offered by Red Baron Oil Tools Rental of Aberdeen, UK as well as the model 2M Cut and Pull System offered by the same company. A wellhead cut and pull spear offered by Baker Oil Tools under product number 122-14 also employs the concept of gripping the internal grooves or threads in a wellhead. Another similar tool is offered by HOMCO and is known as Subsea Wellhead Cutoff and Recovery (SCOR). This tool also grips internally to grooves or threads within the wellhead.
It is thus an object of the present invention to provide a wellhead retrieval tool which is adaptable to any configuration of the wellhead. It is also an object of the present invention to protect the seal bore of the wellhead while the casing cutting operation proceeds. Another object of the present invention is to locate the clutch mechanism outside the flow path of the circulating fluid which brings cuttings out of the wellhead, so as to enhance the reliability of the clutching mechanism. These and other advantages of the present invention will be more readily understood by those skilled in the art from the description of the preferred embodiment below.